This invention relates to the field of metal refining. More particularly, this invention relates to an automatic lance changeover device to which lances are coupled and fixed during steel production by a top blowing process to a vertically displaceable lance carriage.
Over the past few decades, processes have been developed wherein iron melts are desulfurized by the addition of materials which are capable of forming compounds with the sulphur in the melt at high temperatures and under certain reducing conditions. These additive materials are pulverized into granular form and introduced into the melt in suitably proportioned quantities by means of an immersion lance and a carrier gas, preferably argon.
After a certain period of use, the lances used in modern oxygen top blowing processes must be replaced because of wear. An installation for carrying out these replacement operations is described for example in European Pat. No. EP-B 1-0, 112, 540 corresponding to U.S. Pat. No. 4,533,125 assigned to the assigner hereof, all of the contents of which are incorporated herein by reference. Admittedly, in the case of the lances discussed therein, the design concerned is relatively simple, having only one central axial channel for feeding some of the substances required for refining into the molten metal. This does not present significant problems for the leakproof coupling of the upper end of the lance to the feed head for the refining material.
However, in addition to a central axial channel, more highly developed modern lances also have additional channels coaxial to this channel and having an annular cross-section. These channels not only provide the possibility of passing different gas streams through one and the same lance, but also the possibility of cooling the lance, for example with water, for which purpose of course a supply and a discharge channel are required.
Of course, these multichannel lances make far higher demands on the precision of the seal at the coupling between the fluid feed head on the lance carriage with its feed and discharge channels and the associated above mentioned channels in the lance head. A solution to this sealing problem and also a proposal for coupling the upper part of the lance to the fluid feed head, referred to below simply as the coupling head, of the lance carriage are described in patent document LU-69,797 corresponding to U.S. Pat. No. 3,972,515. This proposal consists of fixing the upper part of the lance on the coupling head by means of two swivel bolts and associated nuts.
However, this solution has several disadvantages. First of all, although the manual loosening and tightening of the nuts is not too time-consuming, in view of the location at which this operation takes place, it is associated with a latent accident risk. Furthermore, in the case of a manual changeover operation, there is the expense of holding personnel on call at all times.